Electron beam furnace with magnetically guided axial and transverse beams



Aug. 27, 1963 c. w. HANKS 3,101,515

ELECTRON BEAM FURNACE WITH MAGNETICALLY GUIDED AXIAL AND TRANSVERSE BEAMS Filed June 3, 1960 3 Sheets-Sheet l Pauli 51/2 0 IN VEN TOR.

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ELECTRON BEAM FURNACE WITH MAGNETICALLY GUIDED AXIAL AND TRANSVERSE BEAMS Filed June 3, 1960 3 Sheets-Sheet 2 INVENTOR. (was. (11 flax {5 W 61% fi/wm Aug. 27, 1963 c. w. HANKS 3,101,515

v ELECTRON BEAM FURNACE WITH MAGNETICALLY GUIDED AXIAL AND TRANSVERSE BEAMS Filed June 3. 1960 3 Sheets-Sheet 3 Array/Vin Charles W. Hanks, @rinda, Calif assignor to Stauficr Chemical Company, New York, N .Y.., a corporation of Delaware I Filed June 3, 1950, Ser. No. 33,678 s Claims. (61. 22--57.2)

The present invention relates to an improvement in electron beam furnaces, and particularlyto the improved control and utilizationof electron beam bombardment therein.

It is first to be noted that an electron beam furnace generally comprises a vacuum tank having vacuum-pump ing means attached thereto for continuous evacuating the interior to maintain a relatively constant low pressure therein. Within tank there is disposed a container such as a Water-cooled casting mold having an open top, and adapted to receive and contain metal, or thelike, being operated upon in. the furnace. One or more electron beams are directed into'the upper open end of this casting mold to heat metal therein, and also, electron beams are employed to bombard and progressively melt a metal in the form.- of a melt stock disposed above the mold, so that such metal then drips downward into the top of the mold. Within the top of this mold, there is maintained a molten pool of metal so that, in addition to the general casting function of the furnace, there is also achieved a material purification of the metal being cast.

In connection with the electronbearns employed. in an electron beam furnace of the general type described above,

there have been proposed various methods and apparatus for controlling and directing such electron beams to achieve maximum utility therefrom. In. this respect, attention is invited to prior copending patent application of Hugh R. Smith, Jr, entitled fElectron beam Furnace with United States Patent 3 ,ll,5l5 Patented Aug. 27, 1963 bursts extend generally normal to the melting surface of the metal. Although the interior of the furnace is at all times continuously evacuated to a low pressure, it will be appreciated that very rapid pressure excursions are possible when substantial quantities of gases and vapors are almost instantaneously evolved Within the furnace. It is highly desirable to direct these gases and vapors away from the electron beam sources, for otherwise damage to the latter may occur. In the electron beam furnace configuration of the present invention, the main electron beam bombarding the molten pool of metal is Wholly removed from the area of the melt stock, and is furthermore entirely out of line with the melting surface thereof. Furthermore, the auxiliary electron beam herein provided for bombarding the melt stock, is likewise maintained entirely out of alinement with the melting end of the melt stock. The configuration of the present invention provides for the sub- .stantially complete removal of all electron beam sources Magnetically Guided Beam, filed in the US. Patent Office on May.27, 1960 with Serial No. 32,215, and assigned to the same assignee as the present application, and wherein there are disclosed magnetic guidance'systems providing an improved electron beam furnace. The present invenrtion'is directed to a further improvement in this same field,

main electron beam gun of the furnace may then deposit a substantially all of the energy therefrom into the molten pool in the mold, so as to attain a maxi-mum energy deposition. therein with a minimum size gun. It is also possible, in accordance herewith, to prevent the occurrence of a relatively cooler portion of the molten pool directly below the melt stock being "b o-mbarded. This cooler portion of the molten pool is highly undesirable, and may occur from the interruption of some portion of the electron beam originally directed into the pool. This particular problem is herein overcome by decreasing the diversion of the main pool electron beam by the melt. stock, and furthermore, by theaddition to a particular portion of the pool of further bombarding electrons from the auxiliary orbar beam furnace, there are unavoidably produced gas bursts fromimpurities in the original material being cast therein,

and furthermore, that these pressure excursions or gas from any areas of substantial gas or vapor pressures, as may periodically evolve in the course of melting and casting operations within the furnace. Of particular advantagein the present invention is the utilization of magnetic guidance'fields for directing the main pool electron beam into the upper surface of the mold, and the utilization of this same magnetic field for directing the auxiliary beam onto the melt stock. In accordance with the teaching of the above-noted copending patent application, there is herein employed axial magnetic beam guidance, and there is liurther provided herein for the utilization of this same magnetic guidance field for directing the trajectory of an auxiliary electron beam onto the desired surface of a melt stock for bombardment of same. The present invention lthen incorporates the advantages of the magnetic guidance systems for electron beam furnaces with the further improvement of an auxiliary electron beam for bombarding the melt stock without in any Way reducing the elfectiveness of the main guidance system.

Various objects and advantages of the present invention will become apparent to those skilled in the art from the prior brief description of the features of the present invention, taken together with the following description of particular preferred embodiments hereof; however, no limitation is intended by the terms of this description, and

instead, reference is made to the appended claims for a precise delineation of the true scope of this invention.

The invention is illustrated in the accompanying drawings, wherein:

FIG. 1 is a vertical, sectional view through an electron beam furnace. incorporating the improvements of the present invention;

FIG. 2 is a horizontal, sectional View of the central portion of the electron beam furnace illustrated in FIG. 1, and taken in the plane 2-2 thereof to show the location of the auxiliary electron beam source of this invention;

FIG. 3 is a vertical, sectional "view of an alternative embodiment of the present invention; and

FIG. 4 is a horizontal, sectional view taken in the plane 4-4 of FIG. 3.

Considering first the structural details of an electron beam furnace, as illustrated in FIGS. 1 and 2., it is noted 3 that there is provided a vacuum tank 11 having vacuumpumping means 12 attached thereto and encompassing a casting mold 13. An ingot 14 of cast metal is adapted to be disposed within the casting mold l3 forbombardQ ment by an electron beam 16 from a distant electron gun 17, disposed in substantial vertical displacement above the casting mold. Metal to be cast in the furnace may be.

for moving the bar stock 18 laterally toward thefmold above same, so that electron bombardment of the outer to remove heat therefrom, and the ingot 14 may be continuously withdrawn from the bottom of the mold as by withdrawal means 22.

Magnetic guidance is herein employed to achieve a highly advantageous direction of the main electron beam 16 downward into the open top of the mold onto the top of theingot 14 therein. It will be appreciated that. bombardment of the upper surface of the ingot within the mold will cause the metal thereat to remain molten, so as to form a pool 14 atop the ingot. The magnetic guidancemeans herein employed includes a pair. of identical annular magnet windings 26 and 27 disposed coaxially with the mold with the lower magnet immediately about the mold top, and the upper magnet displaced vertically upward a distance equal to the magnet radius. This particular magnet configuration approximates a Helmholtz coil arrangement so as to thereby establish a magnetic field having parallel lines of force through the annular.

To theextentpreviously described, the electron furnace.

hereof is disclosed in the above-noted copending'patent application, and has been found to produce highly effective casting andpurification operations. The present invention provides for a distinct improvement in the abovedescribed electron beam furnace by the provision of a second or auxiliary electron beam source 41, disposed above thecasting mold 13 and radially outward therefrom. In the particular furnace configuration illustrated, the second beam source or electron gun 41 isdisposed between the two annular magnet coil-s 26 and 27, alongside the bar trough 19. This is best illustrated in FIG. 2, wherein it will be seen that the bar gun, as same may herein be denominated, is disposed immediately adjacent the bar trough 19 radially outward of the mold 13 The particular configurationof the second electron gun gun is to produce a high-energy electron beamdirected in a generally horizontal plane, somewhat inwardly toward the axis of the furnace. The electron gun illustrated includes an electron-emissive cathode wire 42, disposed within a reentrant cavity in a backing electrode 43, and having an anode electrode 44 displaced outwardly of such reentra-nt opening. Energization of the electron-emissive cathode 42 by suitable means, such as a power supply 46, will raise the temperature of this member to electron emission, and the application of a relatively positive potential upon the anode 44 with respect to this cathode and backing electrode 43, as by means of a further power supply 47, will cause such emitted electrons to emerge from thegun in a high-energy beam 48. It will, of course, be appreciated that electron acceleration and beam forming is produced by the establishment of relative potentials between the elements of the. gun, and thus consequently ground connections may be employed as desired, as long .as the anode 44 is maintained at a positive potential with respect to the other portions of the gun. The electron beam 48, established by the second gun 41, is shown as being directed generally circumferentially of the furnace 4 much as the electron beam is traveling generally per pendicularly to the established magnetic guidance field,

there is applied a deflecting force to the beam so as to deflect the trajectory thereof into a generally spiral path, as illustrated. By the utilization of suitable electron beam accelerating potentials and gun placement, the electron thus be seen to likewise herein serve to deflect the trajectory of the second electron beam 48 into direct impingement upon the leading surface of the bar stock 18.

This bombardment of the front face 18. of .the bar stock by the auxiliary or second electron beam 43, as,

same. is deflected by the magnetic guidance field 28, serves to beat this forwardv face and thereby to melt same, so that the bar stock drips downwardly into the open top of the casting mold 13 to form a part of the ingot 14 therein. 1

In this manner, the bar stock has the front race 18' thereof maintained substantially vertical, inasmuch as relatively uniform bombardment of all of such face is achieved by the auxiliary beam. 48. Consequently, gas and vapor bursts which may occur from this front face of the bar,

stock, will be seen to be directed laterally across the upper surface of the mold away from all electron guns in the.

furnace, and preferably, toward the evacuation means of the furnace. The energy employed to melt the bar stock will thus be seen to be'provided by the auxiliary beam 48,

rather than the main beam 16, and consequently, all y energy of this main-beam is thus available for maintaining a relatively eventemperature in the moltenpool 14.

above the ingot, so as to preclude the possibility of relatively cool spots forming in such pool. Despite. the direction of the auxiliary beam'48 in a generally horizontal direction, it will be appreciated that certain portions of the beam will unavoidably traverse paths which are other than horizontal, and consequently, electrons following such paths will then be acted upon by the magnetic held to spiral downwardly into the top of the open mold .13. This further serves to provide additionalbombardment of the molten pool 14 in the casting mold, and con-.

sequently, to insure the presence of a full molten pool therein. 7

An alternative embodiment of the present invention is illustrated in FIGS. 3 and 4, and referring thereto, there will be seen to be provided a pair of metal plates disposed on opposite vertical sides of auxiliary electron gun 41.

I These plates 5-1 and 52 are formed of a ferromagnetic material to serve as magnetic shunts, and may each have i tial advantage of decreasing the amount of electron beam cunvature'in the vicinity of the gun radially outward of the axis of the furnace. In this manner, it is then possible to employ a much lower accelerating potential for the auxiliary electron gun, and yet to attain the desired electron beam trajectory terminating upon the leading face of the bar stock 18. As illustrated in FIG. 4, the electron beam emerging from the gun 41 is subjected to only relatively small magnetic forces throughout the initial portion of the trajectory thereof, and, in fact, until such beam reaches the central axial portion of the furnace whereat the beam enters a very strong magnetic field normal thereto. This strong magnetic field will then deflect the beam trajectory so that the beam is, in fact, curved back around to impinge upon the leading face of the'bar stock. By the magnetic shielding of the auxiliary electron gun, it is herein possibleto materially reduce the requirements imposed-.uponthis gun ,in order to achieve the desired electron beam trajectory therefrom.

It will be appreciated'froma consideration of the location ofthe electron beam gunsof the improved furnace of-tbis invention that same are disposed entirely out of the area of maximum contamination, wherein gun damage may result from bombardment by ions formed in the furnace or from the deposition of vapors thereon, as evolved during the melting'and. casting operations. In particular, it is noted that the auxiliary gun 41 is disposed laterally outward of the ingot and mold on the same Y particular, it is notedthat the auxiliary electron gun even though positioned in somewhat closer proximity to the molten metal than the main 17, i's'likewise fullyprote'cted particularly against ion bombardment, inasmuch as v the ions genenatedimmediately' above the molten pool will generally be'co'nstnained by the guiding magnetic (field to move axially ofthe furnace, rather than radially outward as jrwould be required for same to reach the auxiliary gun. The improvedbar stock melting of "the present invention is thus achieved without any sacrifice in the longevity of the furnace or any other of the advantages accuring to the improved electron beam furnace employing magnetic guidance. a

It will be appreciated that theillustration of the present invention and the above description of particular preferred embodiments thereof have, in part, referred to schematic representations of particular portions of the furnace. 'Inasmuch as such portions form no part of the present invention, and are not novel to this particular furnace, no detailed discussions of same are herein included. With regard to operation of the furnace, same is believed to follow directly from the above description, and the teaching in prior-filed patent applications relative to electron beam furnaces of this general type. A continuous casting process may be performed with the furnace hereof bycontinuously withdrawing the solidified i ingot '14 from the lower portion of the mold 73, while adding molten metal to the top of the ingot to form the pool 14 thereon, which will be seen to solidify as the ingot is slowly withdrawn downwardly through the mold. Likewise, the bar-stock '18 may be continuously fed into the proper position for melting by the auxiliary electron gun 41 by an suitable means such as those schematically illustrated at 2.1; It will be appreciated, in the operation of this furnace, that the feed of the bar stock 18 is adjusted to the energy deposited upon the leading edge thereof by the auxiliary gun 41, so as to maintain the molten metal dripping downwardly into the .pool within the casting mold. Control over the relative feed rates of the bar stock 18 and the withdrawal rate of the ingot Old is left to the discretion of the operator of the particular furnace, and it will be appreciated that the rates employed are dependent, in part, upon the energy of the deposited beam and the particular material being cast in the furnace. #In accordance with prior developements in this field, the electron beam furnace hereof provides not only for the improved casting of high-temperature metals, but furthermore, provides for the purification of same, inasmuch as the high vacuum maintained in the furnace tank serves to remove volatile impuritiesin the metal, and furthermore, the molten pool maintained atop the metal serves to lloat those insoluble impurities which are lighter than the metal being cast.-

What is claimed is: r

1. An electron beam furnace comprising a container for molten metal and having an open top with a vertical axis, means establishing a magnetic field symmetrically about said axis with lines of force converging into the open top of said container, a source of electrons disposed above said containenmeans for accelerating electrons independently of the container and towardsame whereby the accelerated electrons are guided into the container by the converging magnetic field, means feeding a metal melt stock laterally toward said containerimmediately above 1 same and below the source of electrons, an electron gun pingement with said melt stock above the container and to melt "same, means defining a single chamber encompassing at least the'top of said container and said electronsource and electron gun, and means continuously evacuating said chamber.

2. An electron beam furnace as set forth in claim 1,

further defined by means maintaining said magnetic field v substantially axial of said mold for a distance above said mold beyond said second electronbearn source.

3. An electron beam furnace as set forth in claim 1, further defined by magnetic shunt means adjacent said second electron beam source and directing magnetic flux thereabo ut for maintainingv a minimum magnetic field I strength about said second source radially outward of said ing axially from the open top thereof and diverging up wardly for guiding electrons fnom said first gun into the open container to a second electron gun displaced laterally of and above said container and directing an electron beam transversely into said magnetic field for deflection thereby into focus above one side of the container top, the second gun being disposed below the first lgun, means feeding melt stock below the first gun and laterally of said container above same into said second beam focus for bombardment and continuous melting whereby said melt stock drips into said container for further electron bombardment therein, and means for accelerating electrons from the second gun independently of the melt stock transversely into the magnetic field.

5. An electron beam furnace as set forth in claim 4, further defined by means directing said magnetic field about said second electnon gun to maintain a low magnetic field strength thereat.

6. An electron beam furnace as set forth in claim 4, further defined by a pair of ferromagnetic plates disposed one above and one below said second electron gun nadially outward 'fnom said container and connected by a ferromagnetic piece for shunting said magnetic field about said gun and thereby decreasing the beam acceleration required to attain focusing of same upon the metal fed latenally over the container.

7. An electron beam furnace comprising'an annular electron gun having a vertical axis and directing high energyelectrons downward toward such axis, a casting mold having an open top disposed coaxially with said annular gun in spaced relation beneath same, means establishing 'a magnetic field axially through said mold in radial divergence through said annular electron gun for guiding said high energy electrons into the open mold top, means for accelerating electrons from the annular gun independently of the casting mold and toward it, means feeding melt stock below the annular electron gun and laterally toward said axis immediately above said meld, and a laterally displaced electron beam gun disposed adjacent said last means radially of said mold directing electrons transverselyover the mold perpendicularlythnouzghsaid-magneti o field -lfioradeflectionin a curved tnajectory onto a (front rface loi said melt stock'above the mold to melt the I meltustockwherebysame drips downward into the mold I fiorw-furthereleotnon bombardment hoating therein, means .1 for. accelerating electrons from the laterally displaced gun a independently ofrthe rne ltstock feeding means transversely through the magnetic field, landirneans evacuating a chamber encompassingsaidv electron. gunsnrand moldtop for maintaining a [high vacuumtherein.

8.,An electron.laeam iiurnace as set forth in claim 7,

further. chanacterizedlby apair. of magnet pole pieces dis-.

posed :one'lalbloVe and one below. said'laterally displaced electron beamvgunwand connected by a magnetic shunt radially outward of said, gun for establishing a low magnetic field regionlabouttsaidelectron gun anda high magnetic field region radially inward thereof @or establishing said electron beam trajectory onto saidmetal.

9. An electnon-tbeam furnace comprising a mold having an open top, a first annular, magnet .windingv disposed anound themold and adjacent the top out the mold, a sec- 0nd annular, magnet windingspaiced above the firstand disposed anoundflan laxispassing through the mold and first winding to forma Helmholtz ooil arrangement to establish panallel-magnetilc lines 10f fence between the two coils and into the top ot-the mold, the "lines of- :forceconVerging inwardly and downwardly from above the second 7 winding, 2. first electron beam source disposed above the rsecond coil, means for .acceleratingelectnons downwardly land inwardly-from the-first sourcealong the convergmg magnetic lines of force fior guidanceinto the openmold top, means feeding a metal melt stock laterally over said mold from a point between the twocoils, a second elec tron beam source disposed ata level between the first and 1 second coils landlatenallly spaced fnomthe line along which 1 melt stock;is tfed,.1neans tor accelerating-electrons transversely into the magnetic field adjacent said melt stock for deflection by said magnetic field to bombard theleading surface roifis'aidmelt'stock to melt'same, whereby said metal drips fromsaidimelt stock into said mold fior further 1 heating by electron bombardment therein;

1 References Cited in the file of this patent UNITED STATES PATENTS Oandidus Oct. 24, 

1. AN ELECTRON BEAM FURNACE COMPRISING A CONTAINER FOR MOLTEN METAL AND HAVING AN OPEN TOP WITH A VERTICAL AXIS, MEANS ESTABLISHING A MAGNETIC FIELD SYMMETRICALLY ABOUT SAID AXIS WITH LINES OF FORCE CONVERGING INTO THE OPEN TOP OF SAID CONTAINER, A SOURCE OF ELECTRONS DISPOSED ABOVE SAID CONTAINER, MEANS FOR ACCELERATING ELECTRONS INDEPENDENTLY OF THE CONTAINER AND TOWARD SAME WHEREBY THE ACCELERATED ELECTRONS ARE GUIDED INTO THE CONTAINER BY THE CONVERGING MAGNETIC FIELD, MEANS FEEDING A METAL MELT STOCK LATERALLY TOWARD SAID CONTAINER IMMEDIATELY ABOVE SAME AND BELOW THE SOURCE OF ELECTRONS, AND ELECTRON GUN DISPOSED LATERALLY OF THE CONTAINER, MEANS FOR ACCELERATING 